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A. Routray U. C. Mohanty Dev Niyogi S. R. H. Rizvi Krishna K. Osuri 《Meteorology and Atmospheric Physics》2010,106(1-2):107-125
We present the results of the impact of the 3D variational data assimilation (3DVAR) system within the Weather Research and Forecasting (WRF) model to simulate three heavy rainfall events (25–28 June 2005, 29–31 July 2004, and 7–9 August 2002) over the Indian monsoon region. For each event, two numerical experiments were performed. In the first experiment, namely the control simulation (CNTL), the low-resolution global analyses are used as the initial and boundary conditions of the model. In the second experiment (3DV-ANA), the model integration was carried out by inserting additional observations in the model’s initial conditions using the 3DVAR scheme. The 3DVAR used surface weather stations, buoy, ship, radiosonde/rawinsonde, and satellite (oceanic surface wind, cloud motion wind, and cloud top temperature) observations obtained from the India Meteorological Department (IMD). After the successful inclusion of additional observational data using the 3DVAR data assimilation technique, the resulting reanalysis was able to successfully reproduce the structure of convective organization as well as prominent synoptic features associated with the mid-tropospheric cyclones (MTC). The location and intensity of the MTC were better simulated in the 3DV-ANA as compared to the CNTL. The results demonstrate that the improved initial conditions of the mesoscale model using 3DVAR enhanced the location and amount of rainfall over the Indian monsoon region. Model verification and statistical skill were assessed with the help of available upper-air sounding data. The objective verification further highlighted the efficiency of the data assimilation system. The improvements in the 3DVAR run are uniformly better as compared to the CNTL run for all the three cases. The mesoscale 3DVAR data assimilation system is not operational in the weather forecasting centers in India and a significant finding in this study is that the assimilation of Indian conventional and non-conventional observation datasets into numerical weather forecast models can help improve the simulation accuracy of meso-convective activities over the Indian monsoon region. Results from the control experiments also highlight that weather and regional climate model simulations with coarse analysis have high uncertainty in simulating heavy rain events over the Indian monsoon region and assimilation approaches, such as the 3DVAR can help reduce this uncertainty. 相似文献
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During the Intensive Observation Period (IOP) 7 (22 February 1986) of the Genesis of Atlantic Lows Experiment a persistent coastal front was observed along the Carolina coast in the eastern United States. An intensive baroclinic zone, associated with the cold air damming to the east of the Appalachian Mountains, and the warm marine atmospheric boundary layer over the Gulf Stream, resulted in a northeasterly low-level geostrophic wind maximum near the coast.Two convergence zones were observed, one near the shore and the other near the western edge of the Gulf Stream. The convergence zone near the coastline was relatively weaker than that near the Gulf Stream. The differential surface thermal forcing caused enhanced convergence associated with the frontogenesis, and a meso-low was observed over the offshore front. The terms in the frontogenesis equation are estimated, and the diabatic term is found to be larger than the frontogenetic confluence term along the shore. 相似文献
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Sethu Raman Devdutta S. Niyogi A. Prabhu S. Ameenullah S. T. Nagaraj Udai Kumar S. Jayanna 《Journal of Earth System Science》1998,107(1):97-105
Surface features such as soil moisture and vegetation have a profound impact on the surface energy balance and the atmospheric
boundary layer. To quantify this effect for a tropical location, a detailed field experiment, VEBEX, was designed and successfully
executed in a tropical site at Bangalore, India. VEBEX was a joint experiment between the North Carolina State University,
Indian Institute of Science (IISc), and the University of Agricultural Science (UAS) at Bangalore, India. Continuous surface
meteorological measurements were taken over an entire crop period (pre-sowing to post-harvest). During different stages of
the plant growth, intensive observations of surface turbulence, and measurements of physiological and soil moisture measurements
were also conducted. The results obtained provide an insight into the unusually strong variability for the tropics. Interpretation
of the observations and an overview of the analysis procedure and future research initiatives are also presented. 相似文献
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UNCERTAINTY IN THE SPECIFICATION OF SURFACE CHARACTERISTICS: A STUDY OF PREDICTION ERRORS IN THE BOUNDARY LAYER 总被引：1，自引：0，他引：1
The effects of uncertainty in the specification of surface characteristics on simulated atmospheric boundary layer (ABL) processes and structure were investigated using a one-dimensional soil-vegetation-boundary layer model. Observational data from the First International Satellite Land Surface Climatology Project Field Experiment were selected to quantify prediction errors in simulated boundary-layer parameters. Several numerical 12-hour simulations were performed to simulate the convective boundary-layer structure, starting at 0700 LT 6 June 1987.In the control simulation, measured surface parameters and atmospheric data were used to simulate observed boundary-layer processes. In the remaining simulations, five surface parameters – soil texture, initial soil moisture, minimum stomatal resistance, leaf area index, and vegetation cover – were varied systematically to study how uncertainty in the specification of these surface parameters affects simulated boundary-layer processes.The simulated uncertainty in the specification of these five surface parameters resulted in a wide range of errors in the prediction of turbulent fluxes, mean thermodynamic structure, and the depth of the ABL. Under certain conditions uncertainty in the specifications of soil texture and minimum stomatal resistance had the greatest influence on the boundary-layer structure. A lesser but still moderately strong effect on the simulated ABL resulted from (1) a small decrease (4%) in the observed initial soil moisture (although a large increase [40%] had only a marginal effect), and (2) a large reduction (66%) in the observed vegetation cover. High uncertainty in the specification of leaf area index had only a marginal impact on the simulated ABL. It was also found that the variations in these five surface parameters had a negligible effect on the simulated horizontal wind fields. On the other hand, these variations had a significant effect on the vertical distribution of turbulent heat fluxes, and on the predicted maximum boundary-layer depth, which varied from about 1400–2300 m across the 11 simulations. Thus, uncertainties in the specification of surface parameters can significantly affect the simulated boundary-layer structure in terms of meteorological and air quality model predictions. 相似文献
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— Urban terrain poses a challenge for modeling air pollutant diffusion. In tropics, because of the dominant low wind speed environment, the importance of understanding the turbulence diffusion is even more critical, and uncertain. The objective of this study is to estimate the vertical eddy diffusivity of an urban, tropical atmosphere in low–wind speeds. Turbulence measurements at 1 Hz were made at 4-m level over an urban terrain with a roughness length of 0.78 m during winter months. Eddy diffusivity is estimated from spectral quantities of the turbulence data involving turbulent kinetic energy (E) and its dissipation rate (?). The spectral information of the vertical velocity fluctuations is used to estimate the vertical length scale which provides information on the eddy diffusivity. In addition, the product of friction velocity and the vertical length scale has been used to non-dimensionalize the eddy diffusivity, which is shown to increase with increasing instability. Using the eddy diffusivity (K) estimates from the E – ? approach, a relation is suggested for the mixing length based eddy diffusivity models of the form: K = c w .[2.5 ? 0.5(z/L)], where z is the measurement height, L is the Obukhov length, and c w has an average value close to 1 for unstable and near 0.5 for stable conditions for the urban terrains. 相似文献
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The objective of this study is to investigate the impact of a surface data assimilation (SDA) technique, together with the
traditional four-dimensional data assimilation (FDDA), on the simulation of a monsoon depression that formed over India during
the field phase of the 1999 Bay of Bengal Monsoon Experiment (BOBMEX). The SDA uses the analyzed surface data to continuously
assimilate the surface layer temperature as well as the water vapor mixing ratio in the mesoscale model. The depression for
the greater part of this study was offshore and since successful application of the SDA would require surface information,
a method of estimating surface temperature and surface humidity using NOAA-TOVS satellites was used. Three sets of numerical
experiments were performed using a coupled mesoscale model. The first set, called CONTROL, uses the NCEP (National Center
for Environmental Prediction) reanalysis for the initial and lateral boundary conditions in the MM5 simulation. The second
and the third sets implemented the SDA of temperature and moisture together with the traditional FDDA scheme available in
the MM5 model. The second set of MM5 simulation implemented the SDA scheme only over the land areas, and the third set extended
the SDA technique over land as well as sea. Both the second and third sets of the MM5 simulation used the NOAA-TOVS and QuikSCAT
satellite and conventional upper air and surface meteorological data to provide an improved analysis. The results of the three
sets of MM5 simulations are compared with one another and with the analysis and the BOBMEX 1999 buoy, ship, and radiosonde
observations. The predicted sea level pressure of both the model runs with assimilation resembles the analysis closely and
also captures the large-scale structure of the monsoon depression well. The central sea level pressures of the depression
for both the model runs with assimilation were 2–4 hPa lower than the CONTROL. The results of both the model runs with assimilation
indicate a larger spatial area as well as increased rainfall amounts over the coastal regions after landfall compared with
the CONTROL. The impact of FDDA and SDA, the latter over land, resulted in reduced errors of the following: 1.45 K in temperature,
0.39 m s−1 in wind speed, and 14° in wind direction compared with the BOBMEX buoy observation, and 1.43 m s−1 in wind speed, 43° in wind direction, and 0.75% in relative humidity compared with the CONTROL. The impact of SDA over land
and sea compared with SDA over land only showed a further marginal reduction of errors: 0.23 K in air temperature (BOBMEX
buoy) and 1.33 m s−1 in wind speed simulations. 相似文献
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Hwa-Lung Yu Alexander Kolovos George Christakos Jiu-Chiuan Chen Steve Warmerdam Boris Dev 《Stochastic Environmental Research and Risk Assessment (SERRA)》2007,21(5):647-572
This paper describes the spatiotemporal epistematics knowledge synthesis and graphical user interface (SEKS–GUI) framework
and its application in medical geography problems. Based on sound theoretical reasoning, the interactive software library
of SEKS–GUI explores heterogeneous (spatially non-homogeneous and temporally non-stationary) health attribute distributions
(disease incidence, mortality, human exposure, epidemic propagation etc.); expresses the health system’s dependence structure
using (ordinary and generalized) spatiotemporal covariance models; synthesizes core knowledge bases, empirical evidence and
multi-sourced system uncertainty; and generates a meaningful picture of the real-world system using space–time dependent probability
functions and associated maps of health attributes. The implementation stages of the SEKS–GUI library are described in considerable
detail using appropriate screens. The wide applicability of SEKS–GUI is demonstrated by reviewing a selection of real-world
case studies.
An erratum to this article can be found at 相似文献
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Vijayakumar Manghnani Sethu Raman Devdutta S. Niyogi Vinayaka Parameswara John M. Morrison S. V. Ramana J. V. S. S. Raju 《Boundary-Layer Meteorology》2000,97(3):411-430
The variability in boundary-layerstructure over the Indian Ocean during a north-eastmonsoon and the factors influencing it areinvestigated. This study was made possible as acomponent of the Indian Ocean Experiment (INDOEX),conducted from February 19 to March 30, 1998. The dataused are, surface-layer mean and turbulencemeasurements of temperature, humidity and wind, andvertical soundings of temperature and humidity.Significant spatio-temporal variability was observedin the boundary-layer structure throughout the cruise.The ITCZ was characterized as the region withstrongest winds and maximum surface turbulent fluxesof momentum and heat. One of the important findingsfrom this study was a strong influence of continentalair masses on the boundary-layer structure in theNorthern Hemisphere, even at a distance of 600 km offthe Indian coast. This was generally evident in theform of an elevated plume of dry continental airbetween altitudes of 1500 m and 2700 m. Advection ofcontinental aerosols in this layer presents potentialfor significant entrainment into shallow clouds inthis region, which eventually feed deeper clouds atthe ITCZ. This finding provides an explanation foranomalous higher aerosol concentrations found duringprevious studies. The structure of the marineboundary layer was influenced by various factors suchas proximity to land, an anomalous warm pool in theocean and the ITCZ. In the southern hemisphere, theboundary-layer height was primarily governed bysurface-layer sensible heat flux and was found to behighest in the vicinity of the ITCZ. North of theequator it was strongly influenced by land-air-seainteractions. In addition to this synoptic modulation,there was also a significant diurnal variability inthe boundary-layer height. 相似文献